1. FIELD OF THE INVENTION
This invention relates generally to a thermal interface between a semiconductor device and a thermal spreader cap, and, more particularly, to a thermal spreader cap that has a complementary shaped surface to that of the semiconductor device.
2. DESCRIPTION OF THE RELATED ART
Microprocessor devices typically include a semiconductor device or silicon die attached to a substrate. The substrate may be formed from a variety of materials including ceramic and printed circuit boards. These surfaces are generally known as substrates, and the printed circuit-like boards are commonly referred to as organic substrates. Because of the different coefficients of thermal expansion between the silicon die and the substrate it is attached to, the die typically bows away from the substrate, and takes on a convex shape when the die becomes heated, such as during operations. When viewed from the side, this die resembles the "crown" on a curved road.
To assist in dissipating heat generated within the die, a thermal spreader cap is placed on top of or around the die. The thermal spreader cap may be in direct contact with the die, or the thermal spreader cap and the die may have a layer between them, which is referred to as a thermal interface layer. This thermal interface layer in turn may contain a thermal interface material, which is in contact with the die and the side of the thermal spreader cap facing the die. Typically, the thermal interface layer is a highly conductive material that dissipates heat away from the die to the thermal spreader cap.
Under the current approach, the side of the thermal spreader cap that is in direct contact with the die, or the thermal interface material, has a cavity that fits over the processor die, but does not conform to the shape of the processor die. Typically, the cavity is rectangular in shape and forms a box over the bowed die.
Because the typical thermal spreader cap has a box shaped cavity, each point on the surface of the bowed die varies in distance from the thermal spreader cap. Consequently, if there is a thermal interface layer, the thickness of the thermal interface material between the die and the thermal spreader cap varies across the surface of the die. That is, there is more thermal interface material between the thermal spreader cap and the die where the die is closer to the substrate, e.g., at the edges of the die attached to the substrate. Correspondingly, there is less thermal interface material over the portion of the die bowed farthest away from the substrate, e.g., at the center of the processor die.
As a result of the uneven thickness and volume of the thermal interface material, the heat from the die does not dissipate away from the die in a substantially uniform manner. There is an uneven heat flux to the thermal spreader cap from the die that negatively impacts the cooling of the die. Additionally, if the thermal interface material is a liquid, e.g., grease, oftentimes the thermal interface liquid pumps away from the portion of the die surface that is generating the greatest amount of heat. The hottest portion of the die is usually the "crown" of the bowed die, because the heat seeks to dissipate to the thermal spreader cap from the point on the die where there is the least thermal interface material between it and the thermal spreader cap. Therefore, the pumping away of the thermal interface material from this point reduces the heat dissipated from the die. In addition to creating heat dissipation problems, this uneven thickness and volume of thermal interface material also results in an uneven weight load distribution on the die.
The present invention is directed to overcoming, or at least reducing, the effects of one or more of the problems set forth above.